In recent years, along with the increasing awareness of renewable energy, some topics, in particular, the thermoelectric generator (TEG) and the energy harvesting (EH) have become hot research subjects today. For example, based on the trends that the oil will be running out soon and the expensive oil prices, the automotive industry has proposed an issue of enhancing the fuel efficiency one after another. Due to the poor efficiency of the internal combustion engine, about 40% of the oil combusted energy is converted to waste heat expelled, so if the waste heat can be used by recycling through thermoelectric materials, it will be able to improve fuel efficiency up to 8%. It should be noted that the vehicle type thermoelectric generator has an output energy in low voltage and high current form, such as 6 volts and 100 amps.
Many energy sources have with the maximum power point (MPP) characteristic, for example, FIG. 1 shows a characteristic curve of the output current vs. the output voltage of a thermoelectric (TE) energy source (e.g. TEG) and a characteristic curve of the output power vs. the output voltage of a TE energy source (e.g. TEG). In the upper part of FIG. 1, the abscissa represents output voltage VTE of the TE energy source and the ordinate represents output current ITE of the TE energy source; in the lower part of FIG. 1, the abscissa represents output voltage VTE of the TE energy source and the ordinate represents output power PTE of the TE energy source. It can be seen from FIG. 1 that the larger the output current ITE of the TE energy source, the smaller the output voltage VTE thereof is. When the output voltage VTE of the TE energy source is set at an operation voltage VOP shown by FIG. 1, the output power PTE achieves the maximum power value PMAX (i.e., the MPP).
Another example is given by FIG. 2 wherein a characteristic curve of the output current vs. the output voltage of a photovoltaic cell (PV cell) and a characteristic curve of the output power vs. the output voltage of a PV cell are illustrated. In the upper part of FIG. 2, the abscissa represents output voltage VPV of the PV cell and the ordinate represents output current IPV of the PV cell; in the lower part of FIG. 1, the abscissa represents output voltage VPV of the PV cell and the ordinate represents output power PPV of the PV cell. It can be seen from FIG. 2 that the larger the output current IPV of the PV cell, the smaller the output voltage VPV thereof is. When the output voltage VPV of the PV cell is set at an operation voltage VOP shown by FIG. 1, the output power PPV achieves the maximum power value PMAX (i.e., the MPP).
During employing and operating an energy source with the MPP characteristic, it is needed to track the power point on the output of the energy source to advance the power-generating efficiency.